Starting layer dependence of the atomic-layer-deposited HfAlO _xfilms on GaAs

This study reports the effects of the starting layer on the interface and electrical properties of HfAlO _xfilms on GaAs, when the atomic layer deposition (ALD) was performed with tetrakis(ethylmethylamino)hafnium and trimethylaluminum precursors as well as an H ₂O oxidant. By using the Al ₂O ₃-first process, more decrease in the number of Ga-O bonds near the interface region was achieved than by using the HfO ₂-first process, which resulted in a reduction of the interface state density and the frequency dispersion. Furthermore, the Al ₂O ₃-first process decreased the border trap density, as well as the voltage stress-induced electron trapping, as estimated from the hysteresis characteristics of the capacitance-voltage and the leakage current measurement under a ramped-voltage stress condition. Based on these results, we experimentally demonstrate the importance of the cycling sequence during the ALD-HfAlO _xprocess on GaAs.